A typical automobile heater comprises a heat exchanger that is commonly referred to as a heater core. Hot coolant from the automobile engine's cooling system that is allowed to flow through the core exchanges heat to air that is forced across the core. The heated air is discharged into the automobile's passenger compartment. Typically engine coolant is pumped through the heater core from a pump that is driven by the automobile's engine. A heater control valve sets the extent to which the flow is restricted, and hence can control the thermal energy input to the heater.
A typical automobile is powered by an internal combustion engine which has a coolant pump that is engine-driven and circulates coolant through the cooling system. The typical pump is a device whose outlet pressure is related to engine speed. In general, the higher the engine speed, the higher the pump outlet pressure. Variations in coolant pressure within a heater core create varying stresses in the core passageways and at its joints. Certain high pressures that create unacceptably high stresses in the core may occasion core failure. Repeating pressures that individually may not be deemed excessive may, over time, fatigue a core to the point of failure.
One solution to such a potential problem would of course be to make the heat exchanger of heavier materials. Such a solution however adds weight and cost to the automobile at a time when weight and cost savings are especially important to automobile manufacturers. Another solution is to incorporate a pressure limiting, or relief, function that will be effective in limiting the pressure that can be imposed within coolant passageways of a heat exchanger. One example of a relief type function incorporated into a heater control valve is shown in commonly assigned U.S. Pat. No. 4,878,514. This relief function is in the nature of a flow diverter comprising a deflector that increasingly diverts the flow from the core as the pump output increases.
The present invention is directed to a heater control valve embodying a pressure relief function in a new and unique way. The heater control valve is also operated by a proportional solenoid, which allows coolant flow through the core to be better modulated, even to an extent that it may be possible to eliminate from the heater an internal blending door that is used to blend the heated air with non-heated air prior to discharge to the passenger compartment.
Further features, advantages, and benefits of the invention, along with those already mentioned, will be seen in the ensuing detailed description of a presently preferred embodiment representing the best mode contemplated at this time for carrying out the invention.